Subtropical Continents Research Articles

Review on Composition, Nutritional and Medicinal Value of Camel

The camels are the most dominant and widely distributed animal in tropical and subtropical continents of Africa and Asia. They make an important contribution to human survival and utilization of these dry and arid lands. The objective of this review is to describe the general compositions of camel milk and its nutritive and medicinal values. Camels are an important source of milk, meat, hides, wool and serve as a source of prestige for their owners. Camel’s products like milk, meat and urine has nutritional value as well as therapeutic for different human diseases especially in the pastoral communities. Milk is the lacteal secretion of mammary gland of mammals. As it is well known, milk is the first natural food of young mammals during the period immediately after birth. Camel milk is one of the most valuable food resources in the nomadic society and has high nutritive and therapeutic values, due to its essential elements like minerals, vitamins, fatty acids, carbohydrates and protective proteins such as, lactoferrin, lacto peroxidase, lysozme, peptidoglycan recognition protein and immunoglobulins. Camel milk contains disease-fighting immunoglobulins, which are small in size, allowing penetration of antigens and boosting the effectiveness of the immune system. Camel milk has a medicinal properties suggesting that, this milk contains protective proteins, which may have a possible role for enhancing immune defense mechanism. Due to its protective proteins and other components, camel’s milk is important for the treatment of diseases like, dropsy, jaundice, spleen ailment, tuberculosis, asthma, anemia, autoimmune diseases (autism), constipation, crohn’s diseases, and liver cirrhosis also serve as beauty products. Pastoralists have indigenous knowledge in treating their animals and themselves using milk. Because they are living at periphery and remote area where social services are in scarce or even absence and therefore, they depends on traditional medicines. Camel milk is among the items used as traditional medicine in pastoral communities. Generally, Camel milk is extremely nutritious and safe for consumption and has a high therapeutic value, so experimental researches should be conducted specially on the medicinal value of camel milk.

Identification of Annonaceous Acetogenins and Alkaloids from the Leaves, Pulp, and Seeds of Annona atemoya.

Annonaceae is a large family composed of more than 119 genera and more than 2500 species that are distributed in both tropical and subtropical areas. The Annona genus is a member of Annonaceae family, which encompasses about 175 species, most of which are native to Brazil and tropical America. This plant is commonly found on tropical and subtropical continents. Annona atemoya is a commercially important hybrid of A. squamosa and A. cherimola. Phytochemical investigations of A. atemoya leaves, fruit, and seeds have been conducted in limited studies. The purpose of this study was to investigate the constituents of the leaves, fruit pulp, and seeds of A. atemoya because few studies have reported their constituents. Annonaceous acetogenins were identified in the leaves and pulp of A. atemoya for the first time. Twenty compounds were identified: sixteen were acetogenins and four were alkaloids. Additionally, two compounds were isolated, and their structures were confirmed by spectroscopic analysis and compared with the results of previous studies. The concentration of acetogenins in the pulp was very low compared with that in the leaves, whereas the seeds were found to contain the highest concentrations and greatest diversity of compounds.

SIADH (Syndrome of Inappropriate ADH Secretion): Perplexing Look of Dengue Fever

Dengue is a mosquito-borne disease (female mosquitoes of the Aedes genus, principally Aedes aegypti) caused by any one of four closely related dengue viruses. It is endemic in tropical and subtropical continent. World health organization (WHO) currently estimates there may be 50 -100 million dengue infections worldwide every year with over 2.5 billion people at risk of dengue. Symptomatic dengue virus infection may manifests as undifferentiated fever, classical dengue fever (with or without unusual hemorrhages), and dengue hemorrhagic fever (with or without shock). Isolated organopathy or expanded dengue syndrome (EDS) was coined by WHO in the year 2012 to describe cases, which do not fall into either dengue shock syndrome or dengue hemorrhagic fever. The atypical manifestations noted in expanded dengue are multisystemic and multifaceted with organ involvement, such as liver, brain, heart, kidney, central/peripheral nervous system, gastrointestinal tract, lympho reticular system. Dengue virus has long been considered as a non-neurotropic virus, as animal studies have shown that virus does not cross blood brain barrier. Hyponatremia may be found in association with dengue fever and is thought to be caused by peripheral fluid extravasation and resulting intravascular hypovolaemia. But hyponatremia due to syndrome of inappropriate secretion of anti-diuretic hormone (SIADH) in Dengue fever is rare. We report a 40 years old male who was diagnosed as Dengue fever (Dengue Ns1Ag positive) with thrombocytopenia and hyponatremia. He was admitted and further investigations revealed SIADH. He responded well to cautious sodium replacement and addition of tolvaptan. He recovered completely and was discharged after one week. Thus, all clinicians should keep in mind the possibility of SIADH as a part of expanded dengue syndrome.

Dengue: Foreshadowing from Ancient Foe

Dengue is a painful, debilitating mosquito-borne disease(female mosquitoes of the Aedes genus, principally Aedes aegypti)caused by any one of four closely related dengue viruses. It is endemic in tropical and subtropical continent. World health organization (WHO) currently estimates there may be 50 -100 million dengue infections worldwide every year with over 2.5 billion people at risk of dengue. Symptomatic dengue virus infection may manifest as undifferentiated fever, classical dengue fever (with or without unusual hemorrhages), and dengue hemorrhagic fever (with or without shock). Expanded dengue syndrome(EDS) was coined by WHO in the year 2012 to describe cases, which do not fall into either dengue shock syndrome or dengue hemorrhagic fever. The atypical manifestations noted in expanded dengue are multisystem and multifaceted with organ involvement, such as liver, brain, heart, kidney, central/peripheral nervous system, gastrointestinal tract, lympho reticular system.

Expanded Dengue Syndrome Presenting as Acute Pancreatitis

Dengue is a painful, debilitating mosquito-borne disease(female mosquitoes of the Aedes genus, principally Aedes aegypti)caused by any one of four closely related dengue viruses.It is endemic in tropical and subtropical continent. World health organization (WHO) currently estimates there may be 50 -100 million dengue infections worldwide every year with over 2.5 billion people at risk of dengue. Symptomatic dengue virus infection may manifests as undifferentiated fever, classical dengue fever (with or without unusual hemorrhages), and dengue hemorrhagic fever(with or without shock). Expanded dengue syndrome (EDS) was coined by WHO in the year 2012 to describe cases, which do not fall into either dengue shock syndrome or dengue hemorrhagic fever. The atypical manifestations noted in expanded dengue are multisystemic and multifaceted with organ involvement, such as liver, brain, heart, kidney, central/peripheral nervous system, gastrointestinal tract, lympho reticular system. Here we present a case of 35 years old female without any comorbidities who was serologically diagnosed with dengue developed severe upper abdominal pain on 2ndafebrile day and eventually diagnosed as acute pancreatitis both by raised serum lipase and ultrasonographic evidence of swollen pancreas. She was treated conservatively and improved. Thus, all clinicians should keep in mind the possibility of acute pancreatitis as a part of expanded dengue syndrome.

Wetter Subtropics Lead to Reduced Pliocene Coastal Upwelling

AbstractCurrent global warming scenarios suggest surface temperatures may attain warmth last seen during periods of the early‐to mid‐Pliocene (5.3–3 Ma). Pliocene proxy reconstructions suggest sea surface temperatures 3–9°C warmer than today along midlatitude coastal upwelling sites. Recent climate modeling efforts focused on the mid‐Piacenzian period showed a good model‐data fit over midlatitude upwelling regions, but did not attempt to reproduce proxy records of early‐Pliocene warmth. Evidence also suggests that subtropical continents were wetter then; we show that warm coastal SSTs can be explained via such wetter land conditions near the upwelling sites. Using a global atmospheric model, we show that introducing idealized wetter conditions over subtropical continents leads to reductions in upwelling‐favorable wind events by weakening the land‐sea surface pressure gradient. The resulting weaker coastal upwelling of cold deep water can help explain the inferred warm coastal temperatures.

What chance of a sudden stratospheric warming in the southern hemisphere?

Sudden stratospheric warmings (SSWs) are amongst the most dramatic events in the Earth’s atmosphere and they drive extreme surface weather conditions. They have been recently linked to the hot and dry weather conditions that favour wildfires over Australia. However, the chance of a southern hemisphere event is unknown because it has only been observed once. Legitimate estimation of the frequency of SSW events requires a large sample of realistic model simulations. Here we show that the chance of an event is close to 4% per year, implying that an event will occur, on average, every 25 yr, using a state-of-the-art model that simulates SSWs accurately. It is thus not surprising that there was a near miss in the September prior to the Australian wildfire of 2019, given the 40 yr of comprehensive satellite records and just one observed Antarctic event. According to this new estimate, it would also not be surprising to see a second SSW event in the coming years in the southern hemisphere. Such a stratospheric warming event might bring further extreme surface weather conditions and natural hazards, as it may raise the risk of increased rainfall in the latitudinal band of 35–50°S. Meanwhile, the associated hot and dry weather conditions over austral subtropical continents might increase the risk of wildfires over these regions.

The Phytochemical Constituents and Pharmacological Activities of Annona atemoya: A Systematic Review.

Annona atemoya also known as the custard apple is a hybrid between two Annonaceae species: Cherimoya (Annona cherimola) and the sugar apple (Annona squamosa). It is widely cultivated in tropical and subtropical continents including north and south America, Asia, Africa and Australia. Despite becoming an increasingly important commercial fruit plant due to its’ creamy succulent flesh, compared to other Annonaceae species relatively few studies have investigated the phytochemistry and bioactivities of A. atemoya. Studies that evaluated A. atemoya extracts and its constituents were searched through the databases Scopus, Pubmed and Embase from inception to June 2020. Constituents of A. atemoya include alkaloids, flavonoids, terpenes and acetogenins. The results indicate that the constituents of A. atemoya possess cytotoxic, anti-angiogenic, hypolipidemic, antioxidant, anti-inflammatory and neuroprotective activities. However, many of these studies are currently limited in quality and further phytochemical and pharmacological studies are required.

Geographical distribution of extreme deep and intense convective storms on Earth

Vigorous convective storms can not only produce severe destructive weather events and lead to huge damages, but also play a vital role in stratosphere–troposphere exchange (STE). Based on 16-yr Tropical Rainfall Measuring Mission (TRMM) observational data, global geographical distribution of extremely deep and intense convective storms has been investigated. The results show that convective storms are mainly distributed in the tropics, with the largest storm event density located in tropical Africa, tropical Americas and the Maritime Continent. However, compared to convective storms, the most intense and deepest convective storms present a distinctly different geographical distribution pattern, which is true even if the same convective storm samples are used. Overall, tropical Africa is the only region in the world where the distributions of deep and intense convective storms overlap. Other than that, convective storms in the Maritime Continent region are characterized by large convective depth but weak convective intensity, while the opposite is true in subtropical land regions. The top 1% deep convective storms occur most frequently in boreal winter (48%) and spring (36%), and are mainly distributed in the Maritime Continent and tropical Africa. Those most intense convective storms show a weak seasonal variation in quantity while their distributions are significantly different from season to season. Further analysis reveals that convective properties of storms in different regions are distinctly different, and even different in the same region such as tropical Africa but in different seasons. This result suggests that although the formation of convective storm requires sufficient water vapor supply and instable atmospheric conditions, deep convection needs more water vapor supply to develop compared to intense storms. • The geographic distributions of deep and intense convective storms exhibit distinctly different patterns. • Convective storms are strong in convective depth in maritime continent, but strong in convective intensity in subtropical continent. • Deep convection is more likely to occur in a more humid environment than intense storms.

Modulation of Monsoon Circulations by Cross-Equatorial Ocean Heat Transport

Abstract Motivated by observations of southward ocean heat transport (OHT) in the northern Indian Ocean during summer, the role of the ocean in modulating monsoon circulations is explored by coupling an atmospheric model to a slab ocean with an interactive representation of OHT and an idealized subtropical continent. Southward OHT by the cross-equatorial cells is caused by Ekman flow driven by southwesterly monsoon winds in the summer months, cooling sea surface temperatures (SSTs) south of the continent. This increases the reversed meridional surface gradient of moist static energy, shifting the precipitation maximum over the land and strengthening the monsoonal circulation, in the sense of enhancing the vertical wind shear. However, the atmosphere’s cross-equatorial meridional overturning circulation is also weakened by the presence of southward OHT, as the atmosphere is required to transport less energy across the equator. The sensitivity of these effects to varying the strength of the OHT, fixing the OHT at its annual-mean value, and to removing the land is explored. Comparisons with more realistic models suggest that the idealized model used in this study produces a reasonable representation of the effect of OHT on SSTs equatorward of subtropical continents, and hence can be used to study the role of OHT in shaping monsoon circulations on Earth.

An evaluation of East Asian summer monsoon forecast with the North American Multimodel Ensemble hindcast data

AbstractThe abilities of three models (Climate Forecast System version 2 [CFSv2], Canadian Coupled Climate Model version 3 [CanCM3] and Canadian Coupled Climate Model version 4 [CanCM4]) in the North American Multimodel Ensemble for the East Asian summer monsoon (EASM) forecast were evaluated with their 29‐year hindcast data (1982–2010). Many EASM features including monsoon precipitation centres, large‐scale monsoon circulations and monsoon onset and retreat are generally captured by the three models and their ensemble mean, and the multimodel ensemble has the best performance. Since the East Asian domain includes the tropical western North Pacific summer monsoon (WNPSM) and the subtropical continent monsoon, two well‐known monsoon indices, the WNPSM index (WNPSMI) and EASM index (EASMI), and their associated low‐level winds and precipitation anomalies are well forecasted by the models. However, the forecast performance generally decreases as the leads increase, and the performance of EASMI is not as good as that of WNPSMI. CFSv2 forecasts well at leads up to 6 months whereas the skill of CanCM3 (CanCM4) decreases rapidly when the lead increases to 2 months (3 months). The failure of CanCM3 is mainly attributed to the poor forecast of the relationship of EASMI with the El Niño‐Southern Oscillation and Northern Indian Ocean‐western North Pacific (WNP) sea surface temperature anomaly. However, the causes of the poor forecast of CanCM4 for EASMI require further investigation. Sources of the forecast error (FE), which is the difference between model and observation for monsoon precipitation, are more significant than those of the predictability error (PE), which originates from the initial condition error, indicating that model deficiency plays a dominant role in limiting the EASM precipitation forecast. However, the PE cannot be neglected over the tropical western Pacific in CFSv2, over the WNP in CanCM3 and over the Tibetan Plateau in CanCM4. As the lead time increases, the FE does not remarkably change whereas the PE decreases significantly.

The impact of a continent's longitudinal extent on tropical precipitation

AbstractWe examine how the longitudinal extent of a subtropical continent impacts the distribution of tropical precipitation in two aquaplanet general circulation models. In the simpler model, the addition of land decreases evaporation and precipitation in the hemisphere with the continent, and the precipitation response scales with the continent's extent. In the more comprehensive model, tropical precipitation has zonal variation due to the downstream response of clouds to land. As the continental extent increases, this cloud response weakens and the Intertropical Convergence Zone becomes more zonal and shifts to the continent. The different precipitation responses in the two models indicate the importance of radiative feedbacks in modifying tropical circulation in models.

The Precipitation Response to an Idealized Subtropical Continent

Abstract A subtropical continent is added to two aquaplanet atmospheric general circulation models (AGCMs) to better understand the influence of land on tropical circulation and precipitation. The first model, the gray-radiation moist (GRaM) AGCM, has simplified physics, while the second model, the GFDL Atmospheric Model version 2.1 (AM2.1), is a fully comprehensive AGCM. Both models have a continent that is 60° wide in longitude from 10° to 30°N, in an otherwise slab-ocean-covered world. The precipitation response varies with cloudy- and clear-sky feedbacks and depends on continental albedo. In GRaM simulations with a continent, precipitation in the Northern Hemisphere decreases mostly as a result of decreased evaporation. In AM2.1 simulations, precipitation also shifts southward via Hadley circulation changes due to increasing albedo, but the radiative impact of clouds and moisture creates a more complex response. Results are similar when a seasonal cycle of insolation is included in AM2.1 simulations. The impact of a large, bright subtropical continent is to shift precipitation to the opposite hemisphere. In these simulations, the hemisphere of greater tropical precipitation is better predicted by the hemisphere with greater atmospheric energy input, as has been shown in previous literature, rather than the hemisphere that has higher surface temperature.

ENSO-independent contemporaneous variations of anomalous circulations in the Northern and Southern Hemispheres: The polar-tropical seesaw mode

Using the NCEP/NCAR reanalysis and the ENSO indices from the Climate Prediction Center over the period 1978–2014, we have investigated the contemporaneous circulation variations in the Northern and Southern Hemispheres by performing the singular value decomposition analysis of sea level pressure anomalies (SLPA) after the ENSO signal is regressed out. It is found that there exists a polar-tropical seesaw mode (PTSM) that characterizes with the out of phase fluctuations of SLPA between the polar and tropical regions in the Northern and Southern Hemispheres in boreal winter. This PTSM explains 47.74% of the total covariance of SLPA and is almost independent of ENSO. It demonstrates a long-term trend and oscillation cycles of 2–3 and 4–6 yr. The long-term trend in PTSM indicates that the sea level pressure gradually decreases in the tropics and increases in the polar region with time. This PTSM looks roughly symmetric about the equator besides the seesaw pattern of SLPA between the tropics and polar region in each hemisphere. The disturbances in the geopotential height field in association with the PTSM shows baroclinic features in the tropics whereas equivalent barotropic features in the mid and high latitudes in the troposphere. The anomalous thermal forcing in the tropical region is possibly one of the factors facilitating the formation of this PTSM. Significant global precipitation and temperature anomalies related to the PTSM are observed. In the positive PTSM phase, precipitation and temperature are higher than normal in southern Europe and the Mediterranean and surrounding areas, but lower than normal in northern Europe and Siberia. Precipitation is higher than normal while temperature is lower than normal in Northeast Asia. Significant temperature and precipitation anomalies possibly occur in the regions of western China, northern India, parts of North America, parts of subtropical Africa, Maritime Continent, and Antarctic. These results are helpful for better understanding of the circulation variations and the mechanisms behind the interactions between the Northern and Southern Hemispheres and the related winter climate anomalies over globe.

Tropical Gravity Wave Momentum Fluxes and Latent Heating Distributions

Recent satellite determinations of global distributions of absolute gravity wave (GW) momentum fluxes in the lower stratosphere show maxima over the summer subtropical continents and little evidence of GW momentum fluxes associated with the intertropical convergence zone (ITCZ). This seems to be at odds with parameterizations for GW momentum fluxes, where the source is a function of latent heating rates, which are largest in the region of the ITCZ in terms of monthly averages. The authors have examined global distributions of atmospheric latent heating, cloud-top-pressure altitudes, and lower-stratosphere absolute GW momentum fluxes and have found that monthly averages of the lower-stratosphere GW momentum fluxes more closely resemble the monthly mean cloud-top altitudes rather than the monthly mean rates of latent heating. These regions of highest cloud-top altitudes occur when rates of latent heating are largest on the time scale of cloud growth. This, plus previously published studies, suggests that convective sources for stratospheric GW momentum fluxes, being a function of the rate of latent heating, will require either a climate model to correctly model this rate of latent heating or some ad hoc adjustments to account for shortcomings in a climate model’s land–sea differences in convective latent heating.

Global genetic differentiation in a cosmopolitan pest of stored beans: effects of geography, host-plant usage and anthropogenic factors.

Genetic differentiation can be promoted allopatrically by geographic isolation of populations due to limited dispersal ability and diversification over time or sympatrically through, for example, host-race formation. In crop pests, the trading of crops across the world can lead to intermixing of genetically distinct pest populations. However, our understanding of the importance of allopatric and sympatric genetic differentiation in the face of anthropogenic genetic intermixing is limited. Here, we examined global sequence variation in two mitochondrial and one nuclear genes in the seed beetle Callosobruchus maculatus that uses different legumes as hosts. We analyzed 180 samples from 42 populations of this stored bean pest from tropical and subtropical continents and archipelagos: Africa, the Middle East, South and Southeast Asia, Oceania and South America. For the mitochondrial genes, there was weak but significant genetic differentiation across continents/archipelagos. Further, we found pronounced differentiation among subregions within continents/archipelagos both globally and within Africa but not within Asia. We suggest that multiple introductions into Asia and subsequent intermixing within Asia have generated this pattern. The isolation by distance hypothesis was supported globally (with or without continents controlled) but not when host species was restricted to cowpeas Vigna unguiculata, the ancestral host of C. maculatus. We also document significant among-host differentiation both globally and within Asia, but not within Africa. We failed to reject a scenario of a constant population size in the recent past combined with selective neutrality for the mitochondrial genes. We conclude that mitochondrial DNA differentiation is primarily due to geographic isolation within Africa and to multiple invasions by different alleles, followed by host shifts, within Asia. The weak inter-continental differentiation is most likely due to frequent inter-continental gene flow mediated by human crop trade.

Genesis of the South Asian High and Its Impact on the Asian Summer Monsoon Onset

AbstractThe formation of the South Asian high (SAH) in spring and its impacts on the Asian summer monsoon onset are studied using daily 40-yr ECMWF Re-Analysis (ERA-40) data together with a climate-mean composite technique and potential vorticity–diabatic heating (PV–Q) analysis. Results demonstrate that, about 2 weeks before the Asian summer monsoon onset, a burst of convection over the southern Philippines produces a negative vorticity source to its north. The SAH in the upper troposphere over the South China Sea is then generated as an atmospheric response to this negative vorticity forcing with the streamline field manifesting a Gill-type pattern. Afterward, the persistent rainfall over the northern Indochinese peninsula causes the SAH to move westward toward the peninsula. Consequently, a trumpet-shaped flow field is formed to its southwest, resulting in divergence pumping and atmospheric ascent just over the southeastern Bay of Bengal (BOB).Near the surface, as a surface anticyclone is formed over the northern BOB, an SST warm pool is generated in the central–eastern BOB. This, together with SAH pumping, triggers the formation of a monsoon onset vortex (MOV) with strong surface southwesterly developed over the BOB. Enhanced air–sea interaction promotes the further development and northward migration of the MOV. Consequently, the wintertime zonal-orientated subtropical anticyclone belt in the lower troposphere splits, abundant water vapor is transported directly from the BOB to the subtropical continent, and heavy rainfall ensues; the atmospheric circulation changes from winter to summer conditions over the BOB and Asian summer monsoon onset occurs.

Hadley Circulation Response to Orbital Precession. Part II: Subtropical Continent

Abstract The response of the monsoonal and annual-mean Hadley circulation to orbital precession is examined in an idealized atmospheric general circulation model with a simplified representation of land surface processes in subtropical latitudes. When perihelion occurs in the summer of a hemisphere with a subtropical continent, changes in the top-of-atmosphere energy balance, together with a poleward shift of the monsoonal circulation boundary, lead to a strengthening of the monsoonal circulation. Spatial variations in surface heat capacity determine whether radiative perturbations are balanced by energy storage or by atmospheric energy fluxes. Although orbital precession does not affect annual-mean insolation, the annual-mean Hadley circulation does respond to orbital precession because its sensitivity to radiative changes varies over the course of the year: the monsoonal circulation in summer is near the angular momentum-conserving limit and responds directly to radiative changes; whereas in winter, the circulation is affected by the momentum fluxes of extratropical eddies and is less sensitive to radiative changes.

Importance of the subgrid-scale turbulent moist process: Cloud distribution in global cloud-resolving simulations

This study investigated the turbulent transport process within the nonhydrostatic icosahedral atmospheric model (NICAM), a global cloud-resolving model (GCRM), with particular focus on the spatial reproducibility of cloud characteristics in NICAM simulations. A turbulent closure model was applied, based on level 2 of the model developed by Nakanishi and Niino ([Nakanishi, M., and Niino, H., 2006: An improved Mellor–Yamada level-3 model: its numerical stability and application to a regional prediction of advection fog. Boundary-Layer Meteorol., 119, 397–407.]; a revised version of the original Mellor–Yamada model), together with a subgrid-scale condensation process. NICAM simulations were conducted for boreal summer of 2004 using mesh sizes of about 14 km and 7 km. Simulated cloud amounts and radiative budget were compared with observed data. The results confirmed an improvement in the spatial distribution of low clouds that develop in offshore regions of subtropical continents compared to past NICAM experiments ([Iga, S., Tomita, H., Tsushima, Y., and Satoh, M., 2007: Climatology of a nonhydrostatic global model with explicit cloud process. Geophys. Res. Lett., 34, L22814, doi:10.1029/2007/GL031048.]). A sensitivity study of subgrid-scale clouds in the turbulent closure scheme revealed that the turbulent transport process modulated by the subgrid-scale cloud strongly controls not only the low-cloud amount but also mid- and high-cloud amounts. This indicates that parameterization of unresolvable subgrid-scale clouds remains an important component of cloud behavior in GCRMs.

Precipitation interannual variability in South America from the WCRP-CMIP3 multi-model dataset

The ability of coupled climate models from the WCRP-CMIP3 multi-model dataset to reproduce the interannual seasonal variability of precipitation in South America and the influence of the Southern Annular Mode (SAM) and El Nino-Southern Oscillation (ENSO) on such variability is examined. Models are able to reproduce the northward migration of the precipitation variability maximum during autumn and winter and its later return towards the south during spring and summer as well as the high variability throughout the year in southern Chile. Nevertheless, most of them have problems in representing accurately the variability associated with the South Atlantic convergence zone during summer and the typical maximum of variability in the subtropical continent during autumn and winter. The annular-like structure characteristic of the SAM influence on the Southern Hemisphere circulation is basically simulated by all models, but they have serious deficiencies in representing the observed relationship between SAM and both precipitation and circulation anomalies in South America. In addition, most of the models are not able to reproduce the typical wavetrains observed in the circulation anomalies in the Southern Hemisphere associated to ENSO. Only few models, previously identified as those with reasonable ENSO representation at the equatorial Pacific, have evidences of such wavetrains. Coherently, they exhibit the best representation of the ENSO signal in the South American precipitation. Results show that considerable improvement in the model representation of the climate variability in South America and in the associated large-scale teleconnections is still needed.